Repeater system



March 8, 1938.` A. 'E BixzHlLl-:Ty ET AL 2,110,284 A REPEATER SYSTEM lv'r sheets-sheet 1 Filed Sept. 5, 1936 /NvE/vroks; e4f- BACHELET BRANDfron/VEP March s, 193s. A', E. BAHELT ET AL, 2,110,284,

RE'IPEATER SYSTEM .Filed Sept. 5, 1936 7.Sheets-Sheet 2 NE' W VOR/fBR/DG/NG POINT Af. BAC/Her INVENTOR$- -sI BRAND ATTORNEY March s, 1938.

AQ E. BACHELET ET AL REPEATER SYSTEM Filed Sept. 5, 1936 7y sheets-sheet4 Il All vvvrrvv N. u rRANsM/TTER Af. BACHELET NVENTORS.

March 8, 1938. A. E. BACHELET ET AL. l 2,110,284

I REPEATER SYSTEM Filed Sept. 5,` 1936 7 sheets-Sheet 5 HG.v 5.

HARTFORD BR/DG//VG POINT i .AE BACHELET /A/L/E/vrofs.-4 5. BRAND A 7'TORA/EV March 8, 1938- A. E. BACHELET Er AL" l2,110,284

REPEAT-ER SYSTEM f Filed sept. V5, 195e 7 sheets-sheet e F IG. 7

A10/Vl 70k/N6 L 000 SPEAKER .21.5. HACHE/ ET WVM/70H5. s. BRAND ATTORNEYMarch 8, 1 938.

A. E. BAcHELET Er AL REPEATER SYSTEM Filed Sept. 5, 1936 7 sheets-sheet7 Bos T oN f mANsM/TTER MIO HAR TFORD V TRANSM/ 7`7'ER V .74.5. BAG/ELUNVNTORS ATQORNEV Patented Mar. 8, 1938 fol-FICE aEPEA'rEa SYSTEM AlbertE. Bachelet, Mount Vernon, and Smart Brand, Bronxville, N. Y., assignorsto Bell Telephone Laboratories,

---N. Y., a. corporation o Incorporated, New York, i' New YorkApplication September 5, 1936, Serial No. 99,564

` s claims.y

This invention relates to telephone transmission systems and moreparticularly to systems for transmitting radio broadcast programs overwires from one broadcasting station to another.

An object of the invention is to provide a simple and ilexibletransmission network, employing one-way amplifiers, for interconnectinga plurality of broadcasting stations whereby any station may assumecontrol of the network and condition all ampliers in the network totransmit from that stationto all other stations and to preventinterference, by any oi' the other stations, as long as said rst stationretains control.'

Other objects and features of theinvention will appear from thefollowing description, claims and appended drawings, Figs. 2 to 9 ofwhich when placed adjacent to one another as shown in Fig. l, show ahypothetical network extending from Chicago in the middle west to Bostonon the eastern seaboard with intermediate bridged connections to localbroadcasting stations along the route and also to points to the south.

In the drawings, Fig. 2 shows a broadcasting station at Chicagoconnected by a program circuit to a bridging point (Cleveland) at whichpoint a local broadcast station is connected.

From Cleveland the circuit continues east to the` next bridging point(New York, Figs. 3, 4, and 5), where a broadcasting station is connectedand where two other circuits are branched, one to the south, Washington,for example, and another to the east. with a bridging point at Hartford(Figs. 6 and 7) where a local station is connected (Fig. 9) and fromwhich point avcircuit is extended to Boston (Fig. 8).

A description of the circuit arrangement, in

accordance with the invention, will now be given.

It will be assumed that the New York studio (Fig. 5) is to transmit aprogram and therefore control key I (Fig. 5) will be operated. When keyI is operated an obvious circuit is closed to operate relay 2 and lightguard lamp 3. Relay 2 operated connects 13D-volt battery, at its loweralternate contacts, to the middle of simplex coil 4 connected across theline between the studio and the nearest bridging point, in this case theNew York toll ofllce. From this point the circuit can be traced to themiddle of the corresponding simplex coil 5 (Fig. 4) at the toll oiiiceor bridging point and from that point over contact 6 of relay 'I,winding of relay 8 and contacts of key 9 to ground. Relay 8 operates inthis circuit and closes its contact I thereby connecting 13D-Voltbattery I 53 to the mid-point of simplex coil II bridged across themultiple connection 49 between the amplifiers AI, A2, A3, and A4. RelayI2 connected to this simplex circuit operates and lights cue lamps I3 asan indication to the attendant at the bridging'point that one of thestudios has control of the circuit. Operation of relay 8 also closes itscontact I4 and short-circuits the normally operated relay I5 oiamplifier A3 which relay thereupon releases. When relay I5 releases itcloses its contacts I6 therebyclosing a circuit to operate amplifierrelay I'I. vRelay I5 in releasing also opens the circuit for normallylighted direction lamp I8 and the operation of relay I'I lights theopposite direction lamp I 9 which indicates to the attendant thatamplifier A3 is now reversed and set to transmit from its associatedstudio into the network. Operation of relay I1 connects ground at itsinnermost upper contacts to place a second short circuit around relay I5thereby holding relay I5 released in case the contact key` I at the NewYork studio should be released thereby removing battery irom the simplexcircuit and releasing relay 8 which `would' remove ground, at itscontacts I4, from relay I5.'

It should be here pointed out that the-amplifiers at the bridging point,i. e. Cleveland (Fig. 2), New York (Figs. 3 and 4) identified as AI, A2,A3 and A4 and Hartford (Figs. 6 and 7) identi- `iled as BI, B2 and B3,are arranged to normally transmit from left to right, i. e., theleft-hand switching relays, for example relay 39 of amplifier A2 (Fig.3) are normally operated and the right-hand switching relays, forexample relay 4l) of ampliner A2 (Fig. 3), are normally released.Thiscondition will be indicated to the attendant at the bridging pointor repeater station by the lighting of the direction lamps associatedwith the respective relays, for example lamp 4I associated with. relay39 of amplifier A2. When an amplifier is reversed, i. e. arranged totransmit in the opposite direction, the left-hand switching relay isreleased and the right-hand relay operated as in the case just describedin connection with amplifier A3, whereupon normally lighted directionlamp I8, for example, is extinguished and direction lamp IT is lighted.C

Continuing with the circuit description, release of relay I5 closes, atits contacts 42, a

-circuit to operate equalizer relay 43 which operates and connects theequalizing network 44 in shunt to the primary winding of inputtransformer 45 which feeds the amplier tube 46, this equalizing networkbeing for the purpose of compensating for transmission distortionintroduced in the program signalfrequencies by the circuit over whichthey arrive at the ampliiler.: in this case, the line 2l from the NewYork studio. Keys 41 and ll are for manually controlling the equalizerrelay I3. Corresponding relays, equalizing networks and keys areassociated with each of the other amplifiers.

Whenrelay 8 (Fig. 4) operated, and connected 13o-volt battery to themiddle of simplex coil Il, current flowed over the multiple connectionleads 49 in parallel whereupon relay 28v of am- -pliiler A2 and thecorresponding relays of amf pliiiers Ai and A4 operate in a circuitincluding contacts OI .of relay B2, in the case of ampliiier A2. Relay2lin operating vcloses its contacts and operates relay 21 in an obviouscircuit. Relay 21 operated connects, at its contact 2|, 13D-voltbatteryto the middle of simplex coil 29 and thence over the twoconductors in parallel of cable line 30 to the next eastern bridgingpoint (Hartford) where the circuit may be further traced from-themiddleof simplex coil 3i of ampiifler B2 (Fig. 7) and contact 32 ofrelay 33, winding of relay Il and contact of the switch I5 to'ground.Relay 34 operates in this circuit and at its contacts 5I. short-circuitsrelay II which releases.` Operation of relay M also closes its contactI6- which connects 130-v6it battery to the middle of simplex coil l1 andthence to the multiple connection 52 between the ampliiiers BI, B2, andB3 which causes operation of relay 53. associated with the amplifier BIin a circuit including contact 6l of relay 64 (Fig: 6) and thecorresponding relay associated with amplifier BI (Fig. 7). Also relay 38operates to light cue lamp 29 as an indication tothe Hartford repeaterattendant that the network is in use.

Release of relay 5i of the amplifier B2 extinguishes the direction lamp54, operates equalizer relay which connects the equalizing net- .work 51across the primary windingY of input transformer 59 and operates relay5I which in turn lightsdirectlon lampV 5I. Relay in operating connects,at its contact III, a second short circuit around relay 5I to maintainthis relay released in case relay 34 is released due to release of thecontrol keyI at the New York studio and the consequent sequentialrelease of relays l, 21, and 24. V

n Relay B2 of amplifier BI in operating operates relay 85 ,which relayconnects 13D-voit battery, atlts contact 08, to the mid-point of simplexcoil 61 from which point the circuit can be traced over the conductorsloi line 88 in parallel to the Boston repeater station and to themid-point of the simplex coil 89 vconnected across the line atthat-point (Fig. 8).

From the mid-point of coil 89 the circuit can be traced over contact 1liof relay 1I, and through relay 12 to ground. Relay `12 operates in thiscircuit and opens-its contact 1I thereby preventing the accidentaloperation of the control key 1l at the Boston studio from interferingwith the connection established by the operationf of key I at the NewYork studio as long as key I remains operated.

When battery was connected to the multiple connection I2, (Figs. 6 and'1) by the operation of relay 3l, it also caused relays in amplifier BI,corresponding to relays 53 and 85 of amplifier BI to operate therebyconnecting 13D-volt battery to the line leading to the Hartford studio(Fig. 9)r where it caused operation of relay 16 thereby opening contacts11 of that relay and preventing accidental operation of control key 1lfrom intel'- 'and 21 of amplifier A2 to operate thereby con-` necting13D-volt battery to simplex lines 1l to Cleveland and. ll to the south,respectively. The effect of connecting battery to the line 1| at NewYork is exactly the same as that when battery is` connected to line Ilextending `to Hartford and Boston which is also true with respect toconnecting battery to the line Il extending from the south.

In the case of line 1l 'to Cleveland the circuit operation at theCleveland bridging point (Fig. 2) is exactly thesame as at Hartford(Figs. 6, '1, and 9). From Cleveland a circuit li extends to Chicagowhere the studio circuit functions exactly the `same as the easternterminal of the circuit, i. e. Boston (Fig. 8). In other words batteryconnected to the line II at the Cleveland bridging point extends fromthe midpoint of the simplex coil U2 at Chicago through relay I8 toground which relay operates to prevent accidental or other improperoperation oi' control key Il from effecting the switching of theamplifiers as established by key i at New York, as long as that key isheld operated.

The key I at New York will in practice, be held operated until the endof the New York broad- `'cast at which time it will be released therebyconditioning the network to be reswitched for a program from anotherstudio, for example, .Boston which will be later-described.

It will now be seen that amplifier Ai at the New York repeater stationor bridging point (Pig.

left but all other amplifiers remain set to transmit from left to right,which is their normal setting.

'I'he program transmission circuitv can now be tracedfrom, the studiomicrophone. at New York (Fig. 5') through the associatedamplifier, overcontacts Il and of relay 2l now operated to the New York broadcastingtransmitter 22, it

being noted that whenrelay 2 is operated due to operation of the controlkkey an energizing circuit is closed at its upper contact to operaterelay 2l from battery l1 through relay 2l to ground.

Relay 2l in operating closes its contact 24 thereby closing a holdingcircuit for itself to battery 01 independent of relay 2.

Operation of relay 20 also closed its contacts 8l, It thereby connectingthe microphone 22 to the line 2l extending to the repeater station, Fig.4, where the circuit can be further traced over contacts l! and III ofoperated relay I1 to the primary winding ot repeating coil Il, thesecondary of which is connected to the primary of input transformer I6,the secondary of which supplies the amplifier tube The output circuit oftube It' includes output transformer 92 having a tapped secondary, theentire winding of which being connected to conlductors I2 and thesocalled monitoring tap being connected to conductors 94. The output ofthe tube 46 therefore has two branches, one over conductors 83 carryingthe full gain of the amplifier which can-be traced over contacts 95 and98 of relay |1 and conductors 91 tothe monitoring loud-speaker locatedat the repeater station and the other branch, 94,- of reduced energyoutput, which can be traced over contacts 98 and 99 of relay |1 andconductors |00 to transformer |0|. Conductors are also connected tocorresponding relay contacts of amplifiers AI, A2 and A4 but as therelays of these amplifiers, corresponding to relay |1, are unoperatedthe circuit to these amplifiers is open at this point.

Transformer |0| 'couples conductors |00 to multiple connection 49 and'consequently the output transmission from amplifier A3 is further tracedto the input circuits of amplifiers AI, A2

and A4 over contacts such as contacts |02 and |03 of normally operatedrelay 39 of amplifier A2.

Following the circuit through amplifier A2, for example, thetransmission path extends to the primary of repeating coil |04 andthence through input transformer |05 to amplifier tube |06. The fullenergy output vof tube |06 can be traced through output transformer |01over contacts |08 and |09 of relay 39 and conductors 0 to the cable line30-extending to Hartford where it enters associated amplifier B2, Fig.7, over contacts and ||2 of relay 56, and through repeat.

ing coil ||3 and input transformer 59 to the amplifier tube H4. Fromthe.output of transformer ||5two branches extend, one branch including thefull secondary winding of transformer 5, conductors ||6, contacts ||1and ||0 vof relay 50 and conductors ||9 extend to the monitoringloud-speaker at the Hartford repeater station and the other branch,including only a portion of the secondary winding of trans` former H5,conductors |20, contacts 2| and |22 of relay 56 and conductors |23extends to the 'repeating coil |24 which couples conductors |28 with themultiple connection 52 which is bridged to the left-hand terminals ofall'three amplifiers. Due to the fact that relay 5| of amplifier B2 isreleased the connection is open between conducv tors 52 and thisamplifier, but as relay |25 of amplifier BI and the corresponding relay(not.

shown) of amplifier B3 are normal, i. e., operated the transmissioncircuit now branches in two directions, one branch being over contacts|26A and |21 of relay |25 of amplifier B| to the primary winding ofrepeating coil |28 and thence through input transformer |29 to theamplifier tube |30.y

The loutput of tube |30 includes the transformer |3| which has twobranch-es; one the low` level output, including the tappedportion of thesecondary winding, connected to conductors |32 terminates in resistance|33 over contacts |34 and |35 of relay |25. The other, or high energy ilevel branch of the amplifier output, which includes the full secondarywinding of transformer |3|. is connected to conductor |36 and extendsover contacts |31 and |38, of relay |25 and conductors |39 to line |6extending to the Boston station where it terminates in transmitter |40from which point it goes on the air.

The other branch of the transmission circuit from repeating coil |24 isthrough amplifier B3 from left and right in exactly the same manner asthat just described for amplifier BI and thence over line to theHartford broadcast station where it terminates in the transmitter |4|.v

Returning to the New York repeater station (Figs. 3 and M the lprogramtransmission circuit 'trol key 14 at that point.

can be traced tothe west from repeating'coil |0| through amplifier AIfrom left to right in exactly the same manner as that described inconnection with amplifier A2 of Fig. 3 or BIv of Fig. 6, and thence overline 19 to yCleveland (Fig. 2) where it terminates in an amplifier (notshown) identical with B2, for example, at Hart-ford. The program signalsreceived are amplified by this amplifier, passed to a second amplifiervidentical with BI oi Fig. 6 Aand extend over line 8| to Chicago whereit finally terminates in the mitter |42.

At cleveland a third manner (not shown) but branches in two directions,one through amplifier B| and over line 68 to Boston and the otherthrough amplifier B3 and over line 15 tothe Hartford broadcast station.

At New York the second branch extends to amplifier AI and over line 19to Cleveland where it is branched in two directions, one branch passingover line 8| to Chicago and the other to the Cleveland broadcaststation.

The third branch includes amplifier A4 and line 80 extending to thesouth where it may terminate in another bridging amplifier arrangementandbe branched in two or more directions or it may -extend to andterminate directly in a terminal 'broadcast station such as Washington,for example.

It will be understood that the line 30 fromNew York to Hartford, line 68from Hartford to Boston, line 19 from New York to Cleveland, line 82from Cleveland` to Chicago and line 80 from New York to the south may,and in practice will, include further reversible amplifying meansadapted to be switched or set to transmit in` the direction of theprogram signals under control 'of the key at the studio originating theprogram. These amplii'ying means will be identical with the amplifier-sshown, as before described, and further description appears tobeunnecessary. f

It will now be assumed that when the program being transmitted by theNew York studio is finished and some well known cue signal, 'such as amusical note, is transmitted over thecircuit which will be heard by anattendant of each of the connected broadcast stations, the attendant atNew York will release key and, asBoston is scheduled to transmit for thenext period, an attendant at the Boston studio will operate the conat`New York will release relay 2 thereby disconnectingbattery from themid-point of simplex coil 4 connected across line 2|. Relay 2 inreleasing also opens at its upper contact the original energizingcircuit for relay buty this relay is now held over its own contact 24and consequently dces not release at this time.

Removal of battery from the simplex'circuit comprising line 2| releasesrelay 8 of amplifier A3 which disconnects battery from the mid-point ofsimplex coil and also removes, at its conta'ct |4, the original shortcircuit from relay |5. lay, however, is now short-circuited at theinner` Chicago trans- The release of key This reuppervc'ont'acts ofoperated relay I1 and therefore circuit around this relay closedatcontacts 50 4of falsely operated to operated relay 55. y

The removal of battery from simplex coil 21 relases relay I of amplifierBi and the corresponding relay of amplifier B3. Release of relay 5Ireleases relay 55 which removes battery from simplex coil 51 which, inturn, releases relay 12 at the Boston studio which closes its contacts13 thereby preparing a circuit to operate relay 1|, under control" ofkey 14, which we have assumed will be next operated.

The removal of battery from simplex 'coil 31 aflso causes the sequentialrelease of relays (not shown) in amplifier B8 corresponding to relays 5land 55 of amplifier BI which causes battery to be removed from thesimplex'path over line 15 to the Hartford studio which causes therelease of relay 15.

It will be noted that at all studios other than the one originating aprogram the operation of relays, such as 12 of Fig. 8v and 15 of Fig..9, in addition to opening their upper contacts.' also close their lowercontactsthereby short-circuiting the corresponding switching relays |44and |45 thereby insuring that these relays will not be interrupt theprogram being received and broadcast. Similar relays release in the samemanner at Cleveland and Chicago (Fig. 2) due to disconnection of batteryfrom the midpoint of simplex coil of theANew York amplifier A3.

` As before stated. it will now be assumed that Boston is to originate aprogram for the next broadcast period and therefore when the cue signalis heard by the Boston attendant he will 'operate key 14. With key 14operated, as soon as relay 12 releases. as Just described. a circuit isclosed to operate relay 1| whichconnects battery at its lower contacts,Vto simplex coil 5s and at its upper contacts closes an energizingcircuit for relay |44 which operates and connects the studio microphone|44 through the amplifier to line 8l in multiple with the transmitter|45.

Battery on the simplex circuit of line il can be traced to the mid-pointof coil 51 of the Hartford amplifier Biwhere it operates relay I4 whichconnects battery to simplex coil |41 and short-- circuits relay` |25which releases. The release of relay |25, closes its of amplifier BIwhich is identical with the reversal operation of 4amplier AI as morefullyv battery to simplex coil 3| and. at its contacts |54,short-circuits relay 55 which now releases.

The release of relay 50 opens its contacts 50 thereby removing theremaining short circuit around relayll which relay now reoperates.Amplifier 'false operation of key inner lower contacts, thereby'operating relay |45, thus completing the reversal l B2 is now reversedand arranged to transmit from right to left, i. e., from Hartford to NewYork.

Battery connected to simplex coil |41 operates relays (not shown) inamplifier Bl corresponding to relays |49 and 33 of B2 which connectsbattery over the simplex circuit line at the Hartford 'studio whichoperates relay 15 which again opens contact 11 to prevent 18 frominterfering with the switching arrangement established by key 14 atBoston. Relay 16 in operating closes its lower contacts therebyshort-circuiting relay-'|45 and insuring that it will not be falselyoperated;

As amplifier B3 was not reversed for the preceding broadcastitsswitching relay corresponding to relay 5| of B2 was operated and therelay :corresponding to 58 was released and consequently operation ofthe relay corresponding torelay Il has no effect on the relaycorresponding to relay 56 and the amplifier remains in its normalcondition, i. e., arranged to transmit from left to right into line 13to the Hartford studio. Up to this point it will be noted that amplifierBi'is reversed, i. e., is adapted to transmit from right to'left fromline 6I coming from Boston into the other two amplifiers B2 and BI.-Amplifier B2 which was in a reverse condition. i. e., arranged totransmit from the NewYork line 3l' to the other amplifiers BI and B3during the previous broadcast is now turned around into its normalcondition, i. e.. adapted to transmit from the output of amplier BI intothe New York line Il.

Amplifier BI remains ,in its normal condition, i. e..

Varranged to transmit from the output of amplifier Bi into the Hartfordstudio line 15.

Battery connected to coil Ily of amplifier B2 by the operation of relaypasses over line Il to the New York repeater station and operates relayt2v of amplifier A2 which connects battery toslmplex coil 25andshort-circuits relay 35 which now releases and' in turn operatesrelay 4l thereby completing the reversal of this amplifier andconditioning it'to transmit from right to left, i. e., from line Il intothe other ampliers of the station, i. e., AI, AI, and A4.

Connection of battery at the mid-point of coil 25 operates relay |5| ofamplifier AI which in turn operates relay 1. Relay 1 in operatingconnects battery to the simplex coil 5 and short-circuits relay |1 whichreleases and removes .the short circuit from relay i5 which thereuponreoperates thereby restoring this amplifier toits normal oondition, i.e., for transmission from left to right and into line 2l to the New Yorkstudio. Connection of battery to the simplex coil 5 connected acrossline 2| Icauses relay. |62 at-the New York superimposed on in ampliersAI and A4 corresponding to relays |5| and 1, for example, of amplifierAI which connects battery over the simplex circuit of linev 1s toCleveland and line 55 to thev south, respectively. l

Battery on the simplex of line 1! causes relays. not shown, at Clevelandto operate which connects battery to the -simplex circuit of line Il atChicago and tothe Cleveland studio line for the purpose of locking outthe control keys at these points, key 84 at Chicago, for example. As theamplifier at- Cleveland waspointed in the normal direction, i. e., fromleft -to right to transmit from line 1l to Chicago, and to the Clevelandstudio, this amplifier remains in this condition for` the presentbroadcast which also arrives over line 19.

'Ihe program transmission circuits now estab- -arrangements, employingthe same method and instrumentalities for securing transmission over anetwork in either direction with one-way amplifiers or repeaters may beused if desired with# out departing from the spirit of the presentinvention as covered in the appended claims.

What is claimed is:

l. In a two-Way program transmission system, a plurality of programstations adapted to transmit or receive a program, a repeater station, aline for each lprogram station connected in multiple to allother'station lines at said repeater station, a one-Way voice frequencyamplifier in each line at the repeater station and normally pointedtoward its respective program station, a simplex circuit, comprising theconductors of all said lines, extending from each station to all otherstations, sources of direct current, manually controlled switching meansat each station .for connecting one of said current sources to saidsimplex circuit. means associated with each am-I plifier adapted torepeat said direct current around the amplifier in either direction,other means associated with each amplifier responsive to direct currentarriving over the simplex circuit from. its respective program stationto reverse said amplifier and point it toward theother lines, and othermeans at each station responsive to direct current arriving over thesimplex circuit for disabling the switching means thereat as long assaid incoming current persists.

2. In a program transmission system, a plurality of program stations, aline for each station connected' to all other station lines, one-wayamplifiers in each line, means associated with each amplifier adapted,when operated, to reverse the connection of the amplifier with respect Yto its normal transmission direction in the line, manually controlledswitching means at each station for transmitting a control current overits line to all other lines to actuate all reversing meansassociatedwith amplifiers whichareI normally connected to transmittoward the station at which the switching means is operated, and meansat .each station responsive to the contro-l current received over therespective lines to disable the switching means thereat as long as saidcontrol current is received.

3. In a two-way program transmission system, a plurality of programstations, lines for eachstation connected in multiple to all otherstation lines, a one-way amplifier in each line adapted to be reversedwith respect to its line, relay means associated with each amplifier forreversing the amplifier, manually controlled switching means at eachstation for operating all reversing means associated with ampliers inthe system which are not normally connected to transmit away from thestation at which the switching means is operated, and other means ateach station responsive to operation of av switching means at onestation4 to disable the switching means at each of the other stations aslong as the`switching means at the one station is operated.

4. In a two-way program transmission system, a plurality of programstations, lines i'or each station connected in multiple to all otherstation lines, a one-way ampliflervin each line,'means associated witheachamplier to reverse the pointing of said amplifiers in theirrespective.

lines, manually operated switching means at each station adapted totransmit direct current over all of the lines to operate the reversingmeans associated with amplifiers pointed in the direction of the stationat which thelswltching means is operated,- and other means at eachstation responsive to direct current, transmitted from anotherstation,to prevent transmission of direct current therefrom.

. 5. In a transmission system, a plurality of lines connected togetherat one end and extending to stations at the other ends thereof, a.one-way amplifier in each line, eachamplifler being normally connected,in its respective line, to transmit in the same direction with respectto the convnecting point, means associated with each amplifier toreverse its transmitting direction With're- 'spect to its vassociatedline, manually controlled switching means at each station fortransmitting control current over all of said lines toactuate allamplifier reversing means associated with amplifiers which 4are normallypointed in the directionof the station at which the switching means isactuated, said reversing means being arranged 'to operate only when saidcontrol current is received from the direction ltoward which theassociated amplifier is normally pointed, and means at each stationresponsive to control current transmitted from another station todisable. f

the switching means thereat while said control current is connected tothe line. n

6. In a program transmission system, a plurality of program stations,'aline for each station connected in multiple to all other station lines,one-way'ampliers .connected in each line, sources of control current,manually controlled switching means at each station for connecting oneof said Vcurrent sources to the respective line,

means associated with each amplifier adapted to normally connected totransmit, and other means' at each station responsive to control currentreceived over the respective line to disable the switching means thereatand prevent the connection of other control currents to the line as longe as said first control current is received.

'LA system in accordance with claim 6, in which each of said amplifiershas two output circuits, each of different energy level, and in whichthe higher energy output is normally connected to the line,characterized in this that means are provided responsive when saidamplifier is reversed to disconnect the higher energy output from' theline 'and substitute the lower energy output therefonand to connect thehigher energy output to a monitoring receiver'.

8. A system in accordance with claim 6, in which each amplifier has aninput. circuit and two output circuits, each output circuit being ofamplifier are iirst disconnected from the line and after a momentarydelay the input circuit and the low level output circuits are connectedto the line in the opposite transmission direction.

ALBERT E. SMART BRAND.

